1. Field of the Invention
This invention relates to a method of producing a spark plug including a central electrode having a first chip including a noble metal and an earth electrode having a second chip including the noble metal to have a gap between said first and second chips.
2. Description of the Prior Art
Spark plugs using a noble metal chip at the end of their central electrode to provide a spark gap are known. The use of a noble metal provides a long effective life. U.S. Pat. Ser. No. 5,107,168 discloses a spark plug in which a platinum or platinum alloy attachment member is attached to its central electrode to provide a longer effective life.
In such a prior art spark plug, the bonding process of the noble metal chips to the central electrode and the earth electrode is complicated because positioning of the noble metal chips is required for respective electrodes. Moreover, if there are a plurality of earth electrodes, the welding operation is more complicated because several noble chips must be positioned and bonded.
The aim of the present invention is to provide a superior method of producing a spark plug.
According to the present invention, a first aspect of the present invention provides a method of producing a spark plug including a central electrode having a first chip including noble metal and an earth electrode having a second chip including said noble metal, a spark gap being disposed between said first and second chips, comprising the steps of: preparing a chip including said noble metal; welding said chip to an end of said central electrode and to an end of said earth electrode; and cutting said welded chip to form said first and second chips and said spark gap.
According to the present invention, a second aspect of the present invention provides a method of producing a spark plug including a central electrode having a first chip including noble metal and a plurality of earth electrodes, each having a second chip including said noble metal, spark gaps being provided between said first chip and second chips, comprising the steps of: preparing a chip including said noble metal; welding said chip to an end of said central electrode and to ends of said earth electrodes; and cutting said welded chip to form said first chip and said second chips with said spark gaps.
According to the present invention, a third aspect of the present invention provides a method of producing a spark plug including a central electrode having a first chip including noble metal and a tubular metal housing with an earth electrode having a second chip including said noble metal, a spark gap being provided between said first and second chips, comprising the steps of: preparing a chip including said noble metal having a hole of which opening size corresponds to a cross-sectional size of an end of said central electrode, an outline size of said chip corresponding to distance between said end of said central electrode and an end of said earth electrode; fitting said end of said central electrode to said hole; placing said earth electrode on an end of said tubular metal housing such that said chip is supported by contact with said end of said earth electrode; welding said fitted chip to said end of said central electrode and to said end of said earth electrode; and cutting said welded chip to form said first and second chips and said spark gap.
According to the present invention, a fourth aspect of the present invention provides a method of producing a spark plug including a central electrode having a first chip including noble metal and a tubular metal housing having a plurality of earth electrodes, each earth electrode having a second chip including said noble metal, spark gaps being disposed between said first and second chips, comprising the steps of: preparing a chip including said noble metal; welding said chip to an end of said central electrode; placing a unit member including a plurality of said earth electrodes on one end of said housing such that ends of said earth electrodes are supported by contact with a surface of said chip to position said unit member; welding said unit member to said housing; welding ends of said earth electrodes to said chip; and cutting said welded chip to form said first chip and said second chips with said spark gaps.
According to the present invention, a fifth aspect of the present invention provides a method of producing a spark plug including a central electrode having a first chip including noble metal and having a circular plate shape and an earth electrode having a second chip including said noble metal and having a ring shape surrounding said first chip, a spark gap being disposed between said first and second chips, comprising the steps of: preparing a circular plate chip including said noble metal; welding said circular plate chip to an end of said central electrode and to an end of said earth electrode; and cutting said welded chip to form said first and second chips and said spark gap.
In the fifth aspect, said earth electrode is formed to have one open dome.
In the fifth aspect, said earth electrode is formed to have a plurality of earth electrodes which are arranged to surround said first chip.
In the first, second, fourth, and fifth aspects, said chip has a positioning hole, said method further comprising the step of inserting said end of said central electrode into said positioning hole before welding.
In the first, second, fourth, and fifth aspects, an opening size of said hole is determined in accordance with a cross-sectional size of an end of said central electrode, said method further comprising the step of fitting said end of said central electrode to said hole.
In the first to fifth aspects, if it is assumed that a distance across said spark gap is G, a minimum distance between a discharging surface of said first chip defining said spark gap and a first surface of a first welding portion in said earth electrode resulted by said step of welding and a surface of said earth electrode is L1, and a minimum distance between a discharging surface of said second chip defining said spark gap and a second surface of a second welding portion in said central electrode resulted by said step of welding and a surface of the central electrode is L2, said L1 and L2 are greater than a sum of said G and 0.3 mm.
In the first to fifth aspects, said welded chip is cut by either of discharge process, laser cutting, or wire cutting.
In the first to fifth aspects, said noble metal mainly includes Pt and further includes at least one of Ir, Rh, Ru, Pd, Ni, and W.
In the first to fifth aspects, said noble metal mainly includes Ir and further includes at least one of Pt, Rh, Ru, Pd, Ni, and W.